The gas turbine engine is a vital aviation component. While the heart of this propulsion system is the turbine that converts fuel into mechanical energy, several add on Line Replaceable Units (“LRU”) contribute to the overall health and remaining useful life of the engine. Although some LRUs may not be considered to be engine original equipment manufacturer (OEM) parts, they nevertheless contribute to the prognostic health of the propulsion system. Consequently, any accurate estimate of remaining useful life from a maintenance perspective should account for all such LRUs.
Current LRU fault detection is achieved using built-in-tests (BIT). Unfortunately, BIT merely implements simple threshold checks (i.e., hard faults) without taking a systems perspective of the LRU's impact on the propulsion system. Significant maintenance effort is expended to troubleshoot and isolate in-range (i.e., soft) faults. As a result, in the unlikely event that the component finally fails the result may be an engine shutdown or loss of power control.
A failed LRU can drive maintenance costs and operational interrupts up in two ways: 1) an LRU failure may be misdiagnosed as an engine problem causing the engine to be removed unnecessarily, and 2) the engine must be removed to gain access certain LRUs merely to perform physical maintenance and testing.
Further, most turbine engine fault diagnosis methods are developed with engine performance models that have been validated only under steady-state conditions or with actual engine data at steady-state conditions. Engine models that accurately represent the system in transient conditions are difficult to develop.
Nevertheless, developing fault diagnosis methods designed to operate during transient as well as steady-state operation has several important advantages: (a) certain system faults have a distinct signature during system transient conditions that would not normally be discernible during steady-state conditions; (b) the effect of feedback control action is less dominant during transient conditions than during steady-state conditions, therefore sensor and system faults are more evident during transient conditions; and (c) certain engine component incipient faults are manifest only during transient conditions such as start-up and shutdown (e.g. starter and igniter system faults). Therefore, a more robust approach to developing fault diagnosis methods that explicitly account for transient data is required.